Conductivity processes in deuterated betaine phosphate1-x betaine phosphitex mixed crystals

Studies of the electrical conductivity in solid solutions of the mixed crystal system of deuterated antiferroelectric betaine phosphate (DBP) and ferroelectric betaine phosphite (DBPI) were performed. The dc-conductivity sigma(DC) in the temperature interval between 280 and 400 K is obtained from measurements of the complex dielectric permittivity epsilon* = epsilon' - i epsilon " at frequencies between 1 x 10(-2) Hz < nu < 3 x 10(6) Hz. For all crystals studied an anisotropy of sigma(DC) with respect to two crystallographic directions is found. Moreover, we find a clear dependence of the absolute values of sigma(DC) on the phosphite percentage x, whereas the activation energies calculated from an Arrhenius plot of the quantity sigma(DC)*T against the inverse temperature 1/T differ only slightly. For the system DBP30DBPI70 the conductivity results are related to data on the microscopic behaviour of the deuteron exchange derived from two dimensional H-2 nuclear magnetic resonance (NMR) exchange spectroscopic measurements. An effective charge carrier density is estimated and discussed with respect to the differences between the conductivity and the exchange behaviour for pure deuterated substances.